Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Rajan Sen

Co-Major Professor

A. Gray Mullins

Keywords

Embedded Anodes, Fiberglass, Remote Monitoring, Underwater Epoxy, Underwater Repair

Abstract

This dissertation presents findings from two disparate research projects relating to the cathodic protection (CP) of piles supporting bridge elements. The first was a proof of concept study for developing a new hybrid pile repair system incorporating embedded sacrificial zinc anodes within a fiber reinforced polymer (FRP) wrap. The second was to develop and remotely monitor the performance of magnesium anodes protecting steel H-piles supporting two bridges in Florida.

The hybrid FRP-CP system involved a proof-of-concept laboratory study to refine pressure / vacuum bagging systems for pile repair and to quantify the improvement in the FRP concrete bond. Two different FRP systems, one epoxy based and the other urethane based, were evaluated. Improvement in bond was determined through destructive pullout tests conducted on full-size pile specimens that were wrapped while partially submerged in a fresh water tank. The results showed that pressure led to significant improvement in FRP-concrete bond. Pressure was optimal for the epoxy-based system, while vacuum proved better for the urethane-based system. The pressure system was subsequently used to install FRP over embedded anodes in a field demonstration project where four corroding piles were repaired using the hybrid FRP-CP system. Cathodic protection was provided by embedding eight zinc anodes in each concrete pile. Protection below the water line was provided by bulk anodes. Reference electrodes were installed to monitor the performance of the CP system and data loggers were used to monitor the anodic current. Results from over 12 months of monitoring showed that the hybrid FRP-CP system worked and the current demand of the steel was lower in the FRP wrapped piles compared to the unwrapped control.

Numerical simulations were carried out to determine how the hybrid FRP-CP system could be improved. Initially the investigation focused on determining if bulk anodes alone could be used to provide the required protection. Results showed that while bulk anodes were more effective in FRP wrapped piles, they could not provide adequate protection over the entire splash-zone. In view of this, a preliminary three dimensional finite element analysis was carried out using commercially available software. The analysis showed that anode strips embedded in the pile just beneath the surface may provide adequate protection. Such anodes would be easier to install and are an improvement over the system investigated.

The second project involved the development of a remote monitoring system to assess the performance of a sacrificial anode cathodic protection system used for steel piles on two bridges along I-75 in Florida. The problem was the inexplicable consumption rate of the magnesium anodes. Commercially available systems and sensors were used to successfully monitor the environment and the anodic current of the CP system for over 12 months. A solution for the excess magnesium consumption was proposed through the incorporation of an in-circuit variable resistor that could regulate the current draw from the anode. The system was implemented but its performance will be monitored by the Florida Department of Transportation who assumed responsibility for the equipment. Initial results were promising.

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